Hollow structural steel (HSS) is a type of beam with a hollow rectangular cross-section. It is also called structural tubing or hollow structural section as it is available in other materials than steel. The corners are heavily rounded, typically to a radius of approximately twice the wall thickness. The wall thickness is uniform around the section. They are commonly used in welded steel frames where members experience loading in multiple directions.
Square or rectangular HSS is made the same way as pipe. During the manufacturing process flat steel plate is gradually changed in shape to become round where the edges are presented ready to weld. The edges are then welded together to form the mother tube During the manufacturing process the mother tube goes through a series of shaping stands and cold form's the round HSS (mother tube) into the final round, square, or rectangular shape. Most American manufacturers adhere to the ASTM A500 standard, while Canadian manufacturers follow both ASTM A500 and CSA G40.21
In the oil and gas service industry, there is often a need for transfer cases, power take-offs or split-shaft power take-offs that permit machinery to run from torque generated by a vehicle's main engine or a deck engine. The gear boxes for such transfer cases or power take-offs are typically manufactured by welding flat plate steel into rectangular or square boxes, or by casting the case.